Scientific Highlight October 2010 co-ordinated with the Director of the Institute / Head of Department Institute/ Independent Department / Clinical Co-operation Group / Junior Research Group: Department of Medical Radiation Physics and Diagnostics PSP-Element: G-503600-002 Person to contact for further enquiries: Maria Zankl, zankl@helmholtz-muenchen.de, -2792 Title of the Highlight: Adult reference computational phantoms adopted by ICRP and ICRU Keywords: Computational phantoms, voxel models, Reference Male, Reference Female. Central statement of the Highlight in one sentence: The "Reference Individuals" used in world-wide radiation protection legislation were born and grew up in Neuherberg. Text of the Highlight: Ionising radiation has been a ubiquitous and primordial part of our natural and modified environment, since radionuclides have been present permanently in all organisms. Furthermore, ionising radiation has many technical applications and plays an important role in diagnostic and therapeutic medicine. At high exposures, ionising radiation is known to be detrimental to human health. To protect the health of their citizens against such adverse effects while taking advantage of the many positive effects of ionising radiation, governments worldwide have introduced radiation protection legislation and infrastructure. In this protective legislation the annual doses to organs, which are related to these health risks, are specified and limited for radiation exposures at work places and at home. Since everyone is different in shape, life style and metabolism, legislation uses "reference persons" to predict the organ doses from external and internal (after incorporation of radionuclides) radiation exposures, and specify their reference food basket, metabolism, etc.. The anatomy of the male and female reference individuals has been derived from segmented human CT images with high resolution at the Helmholtz Zentrum München. As starting points, segmented data of such individuals were chosen that closely resembled the reference data with respect to body mass and height. 1
These were then transformed into the reference individuals in three main steps: (1) scaling of the voxel dimensions to meet body height and skeleton volume; (2) adjustment of the individual organs to the reference masses by adding or subtracting voxels; (3) adjustment of the amount of subcutaneous adipose tissue such that the whole body mass agreed with the reference data. The resulting adult computer phantoms are voxel phantoms, that means they consist of a three-dimensional array of cuboid volume elements, arranged in columns, rows and slices. The array entries identify to which organ the corresponding voxel belongs. These phantoms were now adopted by ICRP (International Commission on Radiological Protection) and ICRU (International Commission on Radiation Units and Measurements) and are being distributed to the scientific community by ICRP Publication 110 Adult reference computational phantoms. Thus, they will finally provide the international basis of radiation protection regulations. Publication: International Commission on Radiological Protection (mit Zankl, M., Petoussi- Henss, N.): Adult reference computational phantoms. ICRP Publication 110. Ann. ICRP 39(2) (2009) Taking account of the HMGU mission and vision: The adult reference computational phantoms will provide the international basis for radiation protection legislation. Thus, they will help to permit making use of the beneficial effects of ionising radiation in diagnostic and therapeutic medicine and many other technical applications, while at the same time limiting the adverse radiation effects known to occur at higher dose levels. The internal HMGU co-operation partners with whom the Highlight was compiled, if appropriate: Not applicable. 2
The reference computational phantoms adopted by ICRP and ICRU Requirements for reference computational phantoms Must contain the following organs and tissues: those that are known to be sensitive to ionising radiation ( target regions ) source regions relevant to internal dosimetry Must comply with the adult Reference Male and Reference Female with respect to external dimensions organ masses
Reference Male and Reference Female ICRP has specified their main characteristics: Reference masses for 56 organs, organ groups, and tissues
Reference computational phantoms Method of construction Select segmented voxel models of male and female individual whose body height and mass closely resemble the ICRP 89 reference values Golem : 176 cm, 69 kg (176 cm, 73 kg) Laura : 167 cm, 59 kg (163 cm, 60 kg) Modify these segmented voxel models in several steps Golem Laura
Reference computational phantoms Characterisation Male 176 cm, 73 kg 1.9 million voxels Voxel size: 36.5 mm 3 140 Organ identification numbers 53 different tissue types Female 163 cm, 60 kg 3.9 million voxels Voxel size: 15.2 mm 3
Summary / Conclusions For the first time, the ICRP and ICRU have adopted computational phantoms as official representations of the Reference Male and Reference Female. They are defined to enable calculations of the protection quantities organ and tissue equivalent dose and effective dose. The reference computational phantoms are based on computed tomographic data of real persons. Most relevant source and target regions have been adjusted to their reference mass values with high precision. The reference computational phantoms are being disseminated to the scientific community in the form of ICRP Publication 110 Adult reference computational phantoms, Ann. ICRP 39(2) (2009).